1. Field of the Invention
The invention disclosed broadly relates to wireless communications and more particularly relates to coordinating RF use in multiple, collocated wireless systems sharing RF spectrum.
2. Related Art
The invention disclosed is related to U.S. Pat. No. 5,404,574 to Mathilde Benveniste, issued Apr. 4, 1995, entitled xe2x80x9cApparatus And Method For Non-Regular Channel Assignment In Wireless Communication Systemsxe2x80x9d, assigned to the ATandT Corporation, and incorporated herein by reference.
The invention disclosed is also related to U.S. Pat. No. 5,809,423 to Mathilde Benveniste, issued Sep. 15, 1998, entitled xe2x80x9cAdaptive-Dynamic Channel Assignment Organization System And Methodxe2x80x9d, assigned to Lucent Technologies, Inc., and incorporated herein by reference.
The invention disclosed is also related to U.S. Pat. No. 5,787,352 to Mathilde Benveniste, issued Jul. 28, 1998, entitled xe2x80x9cSystem and method for management of neighbor-channel interference with power control and directed channel assignmentxe2x80x9d, assigned to the ATandT Corporation, and incorporated herein by reference.
Demand for wireless voice and data communications continues growing in all aspects of life and will soon lead to a diverse and complex mixture of cells, found in the most unpredictable RF propagation environments. Such cells may exist in layered configurations that enable greater re-use of the RF spectrum and provide continuity of communication between the cell layers. RF planning for such systems is difficult to do manually. In addition to the planning complexity, the cost of manual RF planning becomes a more substantial portion of wireless communication costs as the cost for base stations of the Wireless Centrex Service decreases. Ideally, one would want wireless systems that can self configure, and layered configurations that involve no elaborate planning and coordination of RF use between cell layers.
Easy installation and readiness for operation are features that appeal to a potential owner/operator of a wireless communication system. The ideal system is one that requires minimal information of the planner, and no tedious measurement and calibration, or even knowledge of the physical location of the base stations. Once the base stations are in place, the system would have the ability and intelligence to set base-station power levels and assign channels autonomously.
As wireless mobile communication becomes a necessary part of our lives, a wide range of public and private spaces are likely to house extensions of the conventional cellular system in the form of overlay systems. A layered configuration offers a practical way to maintain continuity between outdoor and indoor communication. Calls can be handled by the overlay system without the capacity loss penalties associated with the use of a different segment of the RF spectrum. Layered self-configurable wireless systems would have no need to communicate for the purpose of coordinating their respective RF use.
A layered configuration is a hierarchical arrangement that usually involves two systemsxe2x80x94the primary system and the adjunct systemxe2x80x94using the same RF spectrum. The primary system is the original owner of the spectrum. An example of a primary system is the macro-cellular system serving an urban area. The adjunct system typically covers a small area that is naturally shielded from interference from the primary system, as in the case of indoor antennas or low antennas placed on a high-traffic spot surrounded by tall buildings. Provided that the adjunct antennas"" power levels are sufficiently low, interference to the primary system users will be negligible.
A method and system are disclosed for coordinating RF use in primary and adjunct wireless systems which are overlapped or layered in a common geographic area and which share the same the same RF spectrum. The adjunct system includes adjunct base stations defining respective adjunct wireless cells and serving adjunct mobile stations located within the respective adjunct cell. The primary system includes primary base stations defining respective primary wireless cells and serving primary mobile stations located within the primary wireless cell. The adjunct system monitors all RF channels and partitions them into two sets, a set of channels likely to be interference-free and a set of noisy channels. Monitoring can be performed by special monitoring sensors or by the base stations. The adjunct mobile stations may participate in the monitoring step. The adjunct system forms a pool of interference-free channels for use by all adjunct base stations. Channels are assigned to adjunct cells from the interference-free pool. The interference-free channels left unassigned serve as back-up channels in case the assigned channels become noisy. The classification of channel into interference-free and noisy and the assignment of channels to adjunct cells is carried out either by a central controller, or by intelligent base stations working cooperatively as peers.
System initialization consists of a brief calibration phase to classify all of the channels as either likely to be interference-free or to be noisy. During the initialization phase, each adjunct base station performs a series consecutive measurements of all channels both on the up-link and on the down-link frequency. The measurements have a sample size N and are periodically conducted over a testing interval. A sample of measurements of the channel is obtained over the entire adjunct system and the strongest measurement is selected. If it exceeds a specified threshold, the channel is classified as noisy. Otherwise it is deemed interference-free. The magnitude of the sample size and testing interval are based on an error probability analysis.
During system operation when adjunct base stations and mobile units are transmitting, the spectrum monitoring procedure employed depends on whether the monitored channel is currently being used by the adjunct system.
A channel used by the adjunct system is an assigned channel. The spectrum monitoring procedure for assigned channels is as follows. Assigned channels which are bearing calls are active. Active assigned channels are monitored by the adjunct base stations through the measurement of the serving signal strength and the bit-error rate. If a channel has a strong signal and a high bit-error rate, then it is deemed noisy and is replaced by a back-up channel. If a channel has a weak signal and a high bit-error rate, then a hand-off is requested to an adjacent adjunct cell. Assigned channels which are not bearing calls are inactive. Inactive assigned channels are periodically replaced by back-up channels which are monitored as non-assigned channels.
A channel not being used by the adjunct system is an nonassigned channel. The spectrum monitoring procedure for nonassigned channels is as follows. Nonassigned channels are monitored by the adjunct system through the measurement of background noise strength. If a channel has a strong background noise above a predetermined threshold, then it is deemed noisy. If a channel has a weak background noise, then the adjunct base stations must deduce the likelihood of future interference. Interference is usually caused by activity in nearby cells in the primary system. Thus, the adjunct base stations must infer the likelihood of future interference a from past activity in the primary system.
During the operation phase, each adjunct base station, in conjunction with mobile units in its respective adjunct cell, continually monitor the nonassigned channels and their classification is updated if there is a change in the background noise or in the spectrum use by the primary system. In the operation phase, sequential tests of the channel are made, wherein an analysis of the noise or interference signal strength is made after each individual measurement. If the noise or interference signal strength is detected above a specified threshold, then the channel is immediately reclassified as noisy. If a channel currently classified as noisy, has a detected noise or interference signal strength below a specified threshold, then a stopping criterion interval is checked. If the time expired since the first low-noise measurement is less than the stopping criterion interval, then a sampling of additional measurements of the channel are made before changing the classification to interference-free. The magnitude of the stopping criterion interval and the sample size for the additional measurements are based on an error probability analysis.
The resulting self-configuring system coordinates RF use in multiple, collocated wireless systems sharing the same the same RF spectrum in an improved manner.